Magnetism of an excited self-conjugate nucleus: precise measurement of the g factor of the 2(1)(+) state in (24)Mg.

A precise measurement of the g factor of the first-excited state in the self-conjugate (N=Z) nucleus (24)Mg is performed by a new time-differential recoil-in-vacuum method based on the hyperfine field of hydrogenlike ions. Theory predicts that the g factors of such states, in which protons and neutrons occupy the same orbits, should depart from 0.5 by a few percent due to configuration mixing and meson-exchange effects. The experimental result, g=0.538±0.013, is in excellent agreement with recent shell-model calculations and shows a departure from 0.5 by almost 3 standard deviations, thus achieving, for the first time, the precision and accuracy needed to test theory. Proof of the new method opens the way for wide applications including measurements of the magnetism of excited states of exotic nuclei produced as radioactive beams.

Gamma-ray fast-timing coincidence measurements from the 18O+18O fusion-evaporation reaction using a mixed LaBr3-HPGe array.

We report on a gamma-ray coincidence analysis using a mixed array of hyperpure germanium and cerium-doped lanthanum tri-bromide (LaBr3:Ce) scintillation detectors to study nuclear electromagnetic transition rates in the pico-to-nanosecond time regime in 33,34P and 33S following fusion-evaporation reactions between an 18O beam and an isotopically enriched 18O implanted tantalum target. Energies from decay gamma-rays associated with the reaction residues were measured in event-by-event coincidence mode, with the measured time difference information between the pairs of gamma-rays in each event also recorded using the ultra-fast coincidence timing technique. The experiment used the good full-energy peak resolution of the LaBr3:Ce detectors coupled with their excellent timing responses in order to determine the excited state lifetime associated with the lowest lying, cross-shell, Iπ=4- "intruder" state previously reported in the N=19 isotone 34P. The extracted lifetime is consistent with a mainly single-particle M2 multipolarity associated with a f7/2→d5/2 single particle transition.

Observation of isomeric decays in the r-process waiting-point nucleus 130Cd82.

The gamma decay of excited states in the waiting-point nucleus (130)Cd(82) has been observed for the first time. An 8(+) two-quasiparticle isomer has been populated both in the fragmentation of a (136)Xe beam as well as in projectile fission of 238U, making (130)Cd the most neutron-rich N = 82 isotone for which information about excited states is available. The results, interpreted using state-of-the-art nuclear shell-model calculations, show no evidence of an N = 82 shell quenching at Z = 48. They allow us to follow nuclear isomerism throughout a full major neutron shell from (98)Cd(50) to (130)Cd(82) and reveal, in comparison with (76)Ni(48) one major proton shell below, an apparently abnormal scaling of nuclear two-body interactions.